Parallel small computer system interface (SCSI) devices come in three different interface formats: narrow, wide and single connector attachment (SCA). Each of the three interfaces can be either single-ended (SE) input/output (I/O) or differential I/O. The narrow interface devices transfer 8 bits of information at a time, while the wide and SCA interface devices transfer 16 bits of information at a time. In SE devices, each bit is represented by a single line. In differential devices, two lines are required to transfer each bit.
As the demand for higher data transfer rates continues to increase, SCSI standards have changed. Maximum data transfer rates for SCSI, SCSI-2, SCSI-3 (also know as Ultra SCSI), and Ultra SCSI-2 are 5, 10, 20 and 40 Mega bytes per second, respectively, for a narrow I/O SCSI device. For wide and SCA devices, the data transfer rate is twice that of narrow I/O devices. The main advantage of differential over SE is the reduction of the effects of noise and the achievement of longer distance capability.
Further differences in SCSI devices have evolved with the introduction of low-voltage differential (LVD) signal devices, in comparison to conventional high-voltage differential (HVD) signal devices. LVD devices offer increased data transfer rates with minimal power consumption and improved noise immunity. Consequently, as the above discussion illustrates, a wide variety of different SCSI devices exist in the industry today.
According to the SCSI Parallel Interconnect 2 (SPI-2) proposed standard, each I/O line (control and data lines) must be terminated properly at both ends in order to avoid reflections and to maintain the integrity of the signals. Consequently, SE lines are terminated differently than HVD lines (SCSI, SCSI-2, and SCSI-3 devices) and LVD lines (Ultra SCSI-2 devices). The wide variety of different types of devices having different SCSI I/O formats has presented problems in terminating the devices. For example, when manufacturers of SCSI disc drives test the drives in large numbers, great care must be taken to terminate specific types of SCSI drives with the correct type of termination device. If the termination devices are included in a test rack or bed, the particular test rack may then only be able to test specific types of SCSI disc drives. This constrains the manufacturer, requiring dedicated test racks having specific termination devices, and thus increasing costs.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.